Light source apparatus and projection-type display apparatus

ABSTRACT

Provided is a light source apparatus including semiconductor light sources and a current detection resistor connected in series, a power source circuit that allows current to flow thereto, a current detection circuit that detects current flowing to the current detection resistor and outputs a current detection signal, a control circuit that controls the power source circuit such that a voltage of the current detection signal approaches a target value, a bypass circuit connected in parallel to the semiconductor light sources, and including a clamp element having a clamp voltage higher than a maximum voltage during operation of the semiconductor light sources and a bypass resistor connected in series to the clamp element, and allowing current to flow when an open fault occurs in the semiconductor light sources, and detection circuits that respectively detect an open fault in the semiconductor light sources based on an end-to-end voltage of the bypass resistors.

BACKGROUND 1. Technical Field

The present invention relates to a light source apparatus that uses asemiconductor light source such as a laser diode (LD) or a lightemitting diode (LED). Furthermore, the invention relates to aprojection-type display apparatus or the like that uses such a lightsource apparatus.

2. Related Art

For example, in a light source apparatus that uses a plurality of laserdiodes, the laser diodes are connected in series and driven in order forthe brightness of the laser diodes to be uniform and to simplify a drivecircuit. However, in such a case, if there is an open fault in one ofthe laser diodes, current cannot flow to the other laser diodes.

In order to avoid such a situation, the laser diode with the open faultis bypassed and current is allowed to flow to the other laser diodes. Asa related art, JP A-2016-105391 discloses a semiconductor light sourcedrive apparatus that can continue to keep the remaining semiconductorlight source elements on even if a disconnection fault occurs in some ofthe semiconductor light source elements, when a plurality ofsemiconductor light source elements are connected in series and driven.

This semiconductor light source drive apparatus includes, a light sourceunit that has a plurality of light source modules connected in series,each light source module having a switching element and an overdrivevoltage detection circuit, in which a Zener diode and a light emittingelement are connected in series, connected in parallel to at least onesemiconductor light source light element, a direct current power sourceunit that supplies a direct current voltage to the light source unit, aswitching element drive unit that drives conduction/non-conduction ofthe switching element of each light source module, and a control unitthat controls the switching element drive unit such that the switchingelement of the same light source module is made to be conductive inresponse to the detection of light by a light detecting element that isarranged opposing the light emitting element of the light source module.

JP A-2016-105391 is an example of related art (Paragraphs 0007 and 0008,FIG. 1).

According to JP A-2016-105391, because a disconnection fault that occursin a semiconductor light source light element in any of the light sourcemodules is detected by the control unit via the light emitting elementand the light detecting element, it takes time for the control unit tocontrol the switching element drive unit to make the switching elementof that light source module conductive, and the remaining light sourcemodules turn off during that time. Accordingly, in a projection-typedisplay apparatus that uses such a light source apparatus, periods occurin which images cannot be projected.

SUMMARY

A first advantage of some aspects of the invention is to provide a lightsource apparatus that, when an open fault occurs in any of a pluralityof semiconductor light sources that are connected in series, can shortenthe time period for which the other semiconductor light sources areturned off, and can even thereafter output a signal indicating that anopen fault has occurred. Furthermore, a second advantage of some aspectsof the invention is to provide a projection-type display device thatuses such a light source apparatus.

In order to solve at least some of the problems described above, a lightsource apparatus according to a first aspect of the invention has aplurality of semiconductor light sources connected in series, a currentdetection resistor connected in series to the plurality of semiconductorlight sources, a power source circuit that allows current to flow to theplurality of semiconductor light sources and the current detectionresistor, a current detection circuit that detects the current thatflows to the current detection resistor and outputs a current detectionsignal, a control circuit that controls the power source circuit suchthat a voltage of the current detection signal approaches a targetvalue, a plurality of bypass circuits respectively connected in parallelto the plurality of semiconductor light sources, each of the bypasscircuits including a clamp element that has a clamp voltage that ishigher than a maximum voltage during operation of the semiconductorlight source and a bypass resistor that is connected in series to theclamp element, and allowing current to flow when there is an open faultin the semiconductor light source, and a plurality of detection circuitsthat respectively detect an open fault in the plurality of semiconductorlight sources based on an end-to-end voltage of the bypass resistors ofthe plurality of bypass circuits.

According to the first aspect of the invention, when an open faultoccurs in any of the plurality of semiconductor light sources that areconnected in series, the drive voltage that is supplied from the powersource circuit increases, thus making it possible to shorten the timefor which the other semiconductor light sources are turned off becausethe bypass current flows due to a clamp operation of the clamp elementin the bypass circuit that is connected in parallel to the semiconductorlight source with the open fault. Also, the detection circuit detectingan open fault in the semiconductor light source based on the end-to-endvoltage of the bypass resistors makes it possible to even thereafteroutput a signal indicating that an open fault has occurred.

Here, it is desirable that a sum total of the clamp voltages of theclamp elements of the plurality of bypass circuits is smaller than thewithstand voltage of the power source circuit. Thus, the power sourcecircuit can be protected from a fault even if an open fault occurs inall of the plurality of semiconductor light sources.

Also, in each of the plurality of bypass circuits, it is desirable thatthe bypass resistor is connected closer to the ground potential sidethan the clamp element is. In this case, a configuration is possible inwhich each of the plurality of detection circuits operates with thepotential of the ground potential side as a reference, making itpossible to stabilize the detection operation even if the end-to-endvoltage of the semiconductor light source varies.

Furthermore, the clamp element may include a Zener diode that has acathode that is connected to an end of the semiconductor light sourceand an anode that is connected to another end of the semiconductor lightsource via the bypass resistor. Because current is quickly allowed toflow if the voltage that is applied between the cathode and the anode ofthe Zener diode reaches the breakdown voltage, it is possible toimmediately allow current to flow to the other semiconductor lightsources when an open fault occurs in any of the semiconductor lightsources and the drive voltage that is supplied from the power sourcecircuit rises.

In the above, the bypass resistor desirably has a resistance value thatis smaller than a resistance value of the current detection resistor.Whereas the current detection resistor needs to have a certainresistance value in order to accurately detect the current that flows tothe plurality of semiconductor light sources, the bypass resistor onlyneeds to be able to detect whether or not current is flowing to thebypass circuit, thus heat generation can be reduced by lowering theresistance value.

Also, the light source apparatus may further have a plurality of levelshifters that respectively shift a level of the detection signals thatare output from the plurality of the detection circuits, and the controlcircuit may output information relating to an open fault in theplurality of semiconductor light sources based on the detection signalsthat are output from the plurality of level shifters. Thus, if an openfault occurs in any of the plurality of semiconductor light sources, itis possible to notify an external microcomputer or the like about theopen fault.

A projection-type display apparatus according to a second aspect of theinvention has any of the light source apparatuses described above.According to the second aspect of the invention, the reliability of theprojection-type display apparatus can be improved with the use of alight source apparatus that, when an open fault occurs in any of aplurality of semiconductor light sources that are connected in series,can shorten the time period for which other semiconductor light sourcesare turned off, and can even thereafter output a signal indicating thatan open fault has occurred.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an example of a configuration of alight source apparatus according to an embodiment of the invention.

FIG. 2 is a circuit diagram showing an example of a configuration of adetection circuit shown in FIG. 1.

FIG. 3 is a block diagram showing an example of a configuration of aprojection-type display apparatus according to an embodiment of theinvention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following is a detailed description of an embodiment of theinvention with reference to the drawings. Note that the same constituentelements are denoted with the same reference numerals and redundantdescription is omitted.

Light Source Apparatus

FIG. 1 is a circuit diagram showing an example of a configuration of thelight source apparatus according to an embodiment of the invention. Asshown in FIG. 1, this light source apparatus includes a semiconductorapparatus (IC) 100, a plurality of semiconductor light sources 111, 112,. . . that are connected in series, a current detection resistor R0 thatis connected in series to the plurality of semiconductor light sources111, 112, . . . , and a plurality of bypass circuits 121, 122, . . .that are respectively connected in parallel to the plurality ofsemiconductor light sources 111, 112, . . . .

The following describes, as an example, a case in which foursemiconductor light sources 111 to 114 are connected between nodes N1 toN5. Each of the semiconductor light sources 111 to 114 include at leastone of a laser diode (LD) or a light emitting diode (LED), and emitslight at a brightness that corresponds to the size of the suppliedcurrent.

For example, if each of the semiconductor light sources 111 to 114 isconfigured by eight LDs and the forward voltage of each LD is 4 V, themaximum voltage during operation of each of the semiconductor lightsources 111 to 114 will be 32V. The current detection resistor R0 isconnected in series to the semiconductor light sources 111 to 114 and,for example, has a low resistance value of about 50 mΩ to 100 mΩ.

Each of the bypass circuits 121 to 124 includes a clamp element that hasa clamp voltage that is higher than the maximum voltage during operationof the semiconductor light sources that are connected in parallel, and abypass resistor that is connected in series to the clamp element, andthe bypass circuits allow current to flow when there is an open fault ina semiconductor light source. Note that an “open fault” in the presentapplication is not limited to a disconnection of a semiconductor lightsource or the wiring thereof, and is a broad concept that includes astate in which a path of electric current is cut off due to improperinstallation of a semiconductor light source or the like.

FIG. 1 shows Zener diodes D1 to D4 as the clamp elements and bypassresistors R1 to R4 that are respectively included in the bypass circuits121 to 124. For example, the Zener diode D1 has a cathode that isconnected to one end (the upper end in the diagram) of the semiconductorlight source 111 and an anode that is connected to the other end (thelower end in the diagram) of the semiconductor light source 111 via thebypass resistor R1.

Because current is quickly allowed to flow if the voltage that isapplied between the cathode and the anode of the Zener diode reaches thebreakdown voltage, when an open fault occurs in any of the semiconductorlight sources and the drive voltage that is supplied from a power sourcecircuit 10 rises, it is possible to immediately allow current to flow tothe other semiconductor light sources.

The lower limit of the breakdown voltage of each of the Zener diodes D1to D4 is set to a value that is obtained by adding a margin voltage to avoltage that corresponds to the current value that flows at the time ofoperation of the corresponding semiconductor light source withconsideration for variation of the current values and the semiconductorlight sources. In order to prevent a malfunction due to ripples and thelike, it is preferable that the breakdown voltage of the Zener diodes D1to D4 is set at least 30% higher than the maximum voltage during theoperation of the semiconductor light sources.

For example, if the maximum voltage during the operation of thesemiconductor light sources is 32 V (eight LDs connected in series),then the breakdown voltage of the Zener diodes D1 to D4 is set to 42 Vor more. Also, if the maximum voltage during the operation of thesemiconductor light sources is 40 V (ten LDs connected in series), thenthe breakdown voltage of the Zener diodes D1 to D4 is set to 52 V ormore.

On the other hand, there is a need to set the upper limit of thebreakdown voltage of each of the Zener diodes D1 to D4 such that thecurrent that flows to the Zener diodes of the bypass circuits that areconnected in parallel to the semiconductor light sources is within therated current when an open fault occurs in a semiconductor light source.Note that resistors for adjustment may be respectively connected inseries to the Zener diodes D1 to D4.

Each of the bypass resistors R1 to R4 may have a resistance value ofaround 50 mΩ to 100 mΩ, similarly to the current detection resistor R0,but it is desirable that each of the bypass resistors R1 to R4 has aresistance value that is smaller than that of the current detectionresistor R0. Whereas the current detection resistor R0 needs to have acertain resistance value in order to accurately detect the current thatflows to the semiconductor light sources 111 to 114, the bypassresistors R1 to R4 only need to be able to detect whether or not currentis flowing to the bypass circuits 121 to 124, and thus heat generationcan be reduced by lowering the resistance value.

Semiconductor Apparatus

The semiconductor apparatus 100 includes the power source circuit 10, aplurality of detection circuits 21 to 24 that are provided incorrespondence with the plurality of semiconductor light sources 111 to114, a plurality of level shifters (L/S) 31 to 34, a current senseamplifier 40, and a control circuit 50. Note that at least some of theconstituent elements of the semiconductor apparatus 100 shown in FIG. 1may be discrete components or external ICs.

The power source circuit 10 is supplied with power source potentials VDDand VSS from outside of the semiconductor apparatus 100, and allowscurrent to flow to the plurality of semiconductor light sources 111 to114 and the current detection resistor R0 by supplying a drive potentialor a drive current to a node N5. In the present embodiment, the powersource potential VSS is a ground potential (0V), and the power sourcecircuit 10 supplies the drive voltage between the node N5 and a node 0of the ground potential VSS.

Here, the sum total of the clamp voltages of the clamp elements of theplurality of bypass circuits 121 to 124, that is, the sum total of thebreakdown voltages of the Zener diodes D1 to D4, is desirably smallerthan the withstand voltage of the power source circuit 10. Thus, even ifan open fault occurs in all of the plurality of semiconductor lightsources 111 to 114, the power source circuit 10 can be protected frombreaking.

The current sense amplifier 40 is a current detection circuit thatdetects the current that flows to the current detection resistor R0 andoutputs a current detection signal by amplifying the end-to-end voltageof the current detection resistor R0 by a predetermined amplificationratio. The control circuit 50, for example, controls the power sourcecircuit 10 such that the voltage of the current detection signal (anaverage voltage or a voltage in a predetermined period) approaches atarget value through digital dimming or analog dimming. The target valuemay be a fixed value, or may be set by an external microcomputer or thelike.

Because the plurality of semiconductor light sources 111 to 114 areconnected in series, if there is an open fault in one of thesemiconductor light sources, current will not flow to the othersemiconductor light sources. Therefore, a plurality of detectioncircuits 21 to 24 that respectively detect an open fault of theplurality of semiconductor light sources 111 to 114 based on theend-to-end voltage of the bypass resistors R1 to R4 of the plurality ofbypass circuits 121 to 124 are provided.

FIG. 2 is a circuit diagram showing an example of a configuration of thedetection circuit shown in FIG. 1. FIG. 2 shows an example of aconfiguration of the detection circuit 21, and the configuration of thedetection circuits 22 to 24 may be similar. As shown in FIG. 2, thedetection circuit 21 includes a current sense amplifier 25 and acomparator 26, and detects open faults in the semiconductor light source111 (FIG. 1) based on the end-to-end voltage of the bypass resistor R1of the bypass circuit 121. The power source voltage of the detectioncircuit 21 can be supplied from a first node N1 and a second node N2.

The current sense amplifier 25 is constituted by, for example, adifferential amplifier, a single amplifier, or the like, and amplifiesthe end-to-end voltage of the bypass resistor R1 by a predeterminedamplification ratio to generate an output voltage. The comparator 26compares the output voltage of the current sense amplifier 25 to areference voltage VREF. The reference voltage VREF may be generated by afixed voltage circuit or a voltage dividing circuit that is connectedbetween the first node N1 and the second node N2.

Alternatively, if the comparator 26 has an offset, the input conversionvoltage of the offset may be used as the reference voltage VREF. In acase where the comparator that has an offset is used in the plurality ofdetection circuits 21 to 24 (FIG. 1), even if the power source potentialsupplied to the comparator is different, a uniform reference voltage caneasily be generated.

The comparator 26 deactivates a detection signal DET1 to low level whenthe output voltage of the current sense amplifier 25 is smaller thanreference voltage VREF, and activates the detection signal DET1 to highlevel when the output voltage of the current sense amplifier 25 islarger than the reference voltage VREF.

Referring again to FIG. 1, in each of the plurality of bypass circuits121 to 124, it is desirable that the bypass resistors R1 and R4 areconnected closer to the ground potential VSS side than the Zener diodesD1 to D4 that are clamp elements are. In this case, a configuration ispossible in which each of the plurality of detection circuits 21 to 24operates with the potential of the ground potential VSS side as areference, making it is possible to stabilize the detection operationeven if the end-to-end voltage of the semiconductor light sources 111 to114 varies.

For example, if an open fault occurs in the semiconductor light source111, the voltage of the current detection signal that is output from thecurrent sense amplifier 40 decreases because the current that flows tothe current detection resistor R0 decreases. Accordingly, the controlcircuit 50 controls the power source circuit 10 so as to increase thedrive voltage that is supplied to the semiconductor light sources 111 to114.

By increasing the drive voltage supplied from the power source circuit10, in the bypass circuit 121 that is connected in parallel to thesemiconductor light source 111, the voltage between the cathode and theanode of the Zener diode D1 reaches the breakdown voltage and the bypasscurrent flows to the Zener diode D1 and the bypass resistor R1. Thus, itis possible to shorten the time period for which the other semiconductorlight sources 112 to 114 are turned off because current also flows tothose other semiconductor light sources 112 to 114.

The end-to-end voltage of the bypass circuit 121 is maintained at thesum of the breakdown voltage of the Zener diode D1 and the end-to-endvoltage of the bypass resistor R1. In this case, the power consumption(generated heat) of the light source apparatus increases in comparisonto a case in which a short circuit caused by the switching elementoccurs between both ends of the semiconductor light source 111 with theopen fault, but this is tolerable because it is a temporary measure thatlasts until the semiconductor light source 111 with the open fault isreplaced with a new semiconductor light source.

On the other hand, because the power source voltage is supplied from thenode N1 and the node N2 to the detection circuit 21 due to a shortcircuit not occurring between both ends of the semiconductor lightsource 111 with the open fault, the detection circuit 21 continues tooperate and it is possible to detect the open fault of the semiconductorlight source 111 based on the end-to-end voltage of the bypass resistorR1. The detection circuit 21 detects an open fault in the semiconductorlight source 111 and activates a detection signal when the end-to-endvoltage of the bypass resistor R1 exceeds a predetermined value.

The plurality of level shifters 31 to 34 respectively shift the level ofthe detection signals that are output from the plurality of detectioncircuits 21 to 24. Also, the control circuit 50 outputs informationrelating to open faults of the plurality of semiconductor light sources111 to 114 based on the detection signals that are output from theplurality of level shifters 31 to 34.

Thus, when an open fault occurs in any of the plurality of semiconductorlight sources 111 to 114, it is possible to notify an externalmicrocomputer or the like about the open fault. For example, the controlcircuit 50 may generate open fault flags F1 to F4 based on the detectionsignals that are output from the plurality of level shifters 31 to 34,and output the open fault flags F1 to F4 from four terminals of thesemiconductor apparatus 100.

Alternatively, if the plurality of semiconductor light sources 111 to114 are formed as one unit, the control circuit 50 may generate an openfault flag F0 indicating that the detection signal that is output fromone of the plurality of the level shifters 31 to 34 has been activated,and output the open fault flag F0 from one terminal of the semiconductorapparatus 100.

As described above, according to the present embodiment, when an openfault occurs in any of the plurality of semiconductor light sources thatare connected in series, the drive voltage that is supplied from thepower source circuit increases, thus making it possible to shorten thetime period for which the other semiconductor light sources are turnedoff because the bypass current flows due to a clamp operation of theclamp element in the bypass circuit that is connected in parallel to thesemiconductor light source with the open fault. Also, the detectioncircuit detecting an open fault in the semiconductor light source basedon the end-to-end voltage of the semiconductor light source makes itpossible to output a signal indicating that an open fault has occurredeven after current flows via the bypass circuit.

Projection-Type Display Apparatus

The following describes the projection-type display apparatus (videoprojector) according to one embodiment of the invention.

FIG. 3 is a block diagram showing an example of a configuration of theprojection-type display apparatus according to one embodiment of theinvention. A projection-type display apparatus 200 is supplied a powersource voltage from outside, and is supplied image data from an imagedata supply apparatus such as a personal computer or a video player andprojects an image onto a screen (projection surface) 300 based on theimage data.

As shown in FIG. 3, the projection-type display apparatus 200 includes apower source circuit 210, an image data processing unit 220, a controlunit 230, a light source apparatus 240, a panel 250 and a projectionoptical system 260. Here, the light source apparatus 240 is the lightsource apparatus according to one embodiment of the invention, andincludes the semiconductor apparatus 100 and a plurality ofsemiconductor light sources 110 that are connected in series.

The power source circuit 210, for example, based on a power sourcevoltage of AC 100 V that is supplied from outside, generates a DC logicpower source voltage and supplies the DC logic power source voltage tothe image data processing unit 220, the control unit 230, and the like,and also generates a DC power source voltage that is higher than thelogic power source voltage and supplies the higher DC power sourcevoltage to the semiconductor apparatus 100 of the light source apparatus240, and the like.

The image data processing unit 220 and the control unit 230 areconstituted by, for example, at least one microcomputer and the like.The image data processing unit 220 processes image data supplied fromoutside to generate an image signal for display and a synchronizingsignal, and drives the panel 250 and renders the image data by supplyingthe image signal and the synchronizing signal to the panel 250.

The control unit 230 controls the components of the projection-typedisplay apparatus 200 in accordance with the operation of a user that ismade with use of a remote control or a control panel (not shown). If itis possible to adjust the light of the light source apparatus 240, thecontrol unit 230 generates a digital dimming signal DCS or an analogdimming signal ACS, and supplies either the digital dimming signal DCSor the analog dimming signal ACS to the semiconductor apparatus 100 ofthe light source apparatus 240. Thus, the semiconductor apparatus 100controls the light emission operation of the plurality of semiconductorlight sources 110 that are connected in series.

The light source apparatus 240 irradiates light at a brightness that isin accordance with the digital dimming signal DCS or the analog dimmingsignal ACS that is supplied from the control unit 230 and projects thelight onto the panel 250. For example, if the semiconductor light source110 includes a plurality of laser diodes that generate blue light, thelight source apparatus 240 may further include phosphors that receiveblue light that is generated by some of the laser diodes and generateyellow light, and a spectroscopic unit that separates red light andgreen light from the yellow light in accordance with the wavelength. Inthis case, the light source apparatus 240 can generate light in threecolors, namely R (red), G (green) and B (blue).

The panel 250 modulates light that is irradiated from the light sourceapparatus 240, in accordance with the image signal and synchronizingsignal that are supplied from the image data processing unit 220. Forexample, the panel 250 may include three liquid crystal panelscorresponding to the three colors RGB. Each liquid crystal panel formsan image by changing the transmittance of light in a plurality of pixelsthat are arranged in a matrix. The modulated light that is modulated bythe panel 250 is guided to the projection optical system 260.

The projection optical system 260 includes at least one lens. Forexample, the projection optical system 260 is provided with a projectionlens that is a group of lenses for projecting modulated light that ismodulated by the panel 250 onto the screen 300 to form an image, and isprovided with a variety of adjustment mechanisms that adjust theaperture, zoom, shift position, and the like of the projection lenses.These adjustment mechanisms are controlled by the control unit 230. Animage is displayed on the screen 300 by the projection optical system260 projecting the modulated light onto the screen 300.

According to the present embodiment, the reliability of theprojection-type display apparatus 200 can be improved with the use of alight source apparatus 240 that, when an open fault occurs in any of theplurality of semiconductor light sources 110 that are connected inseries, can shorten the time period for which the other semiconductorlight sources are turned off, and can even thereafter output a signalindicating that an open fault has occurred.

The invention is not limited to the embodiments described above, and canbe modified without departing from the technical concept of theinvention by those with ordinary skill in the art.

This application claims priority from Japanese Patent Application No.2018-009439 filed in the Japanese Patent Office on Jan. 24, 2018, theentire disclosure of which is hereby incorporated by reference in itsentirely.

What is claimed is:
 1. A light source apparatus comprising: a plurality of semiconductor light sources connected in series; a current detection resistor connected in series to the plurality of semiconductor light sources; a power source circuit that allows current to flow to the plurality of semiconductor light sources and the current detection resistor; a current detection circuit that detects current that flows to the current detection resistor and outputs a current detection signal; a control circuit that controls the power source circuit such that a voltage of the current detection signal approaches a target value; a plurality of bypass circuits respectively connected in parallel to the plurality of semiconductor light sources, each of the bypass circuits including a clamp element that has a clamp voltage that is higher than a maximum voltage during operation of the semiconductor light source and a bypass resistor that is connected in series to the clamp element, and allowing current to flow when there is an open fault in the semiconductor light source; and a plurality of detection circuits that respectively detect an open fault in the plurality of semiconductor light sources based on an end-to-end voltage of the bypass resistors of the plurality of bypass circuits.
 2. The light source apparatus according to claim 1, wherein a sum total of the clamp voltages of the clamp elements of the plurality of bypass circuits is smaller than a withstand voltage of the power source circuit.
 3. The light source apparatus according to claim 1, wherein, in each of the plurality of bypass circuits, the bypass resistor is connected closer to a ground potential side that the clamp element is.
 4. The light source apparatus according to claim 1, wherein the clamp element includes a Zener diode that has a cathode that is connected to an end of the semiconductor light source and an anode that is connected to another end of the semiconductor light source via the bypass resistor.
 5. The light source apparatus according to claim 1, wherein the bypass resistor has a resistance value that is smaller than a resistance value of the current detection resistor.
 6. The light source apparatus according to claim 1, further comprising a plurality of level shifters that respectively shift a level of the detection signals that are output from the plurality of detection circuits, wherein the control circuit outputs information relating to an open fault in the plurality of semiconductor light sources based on the detection signals that are output from the plurality of level shifters.
 7. A projection-type display apparatus comprising the light source apparatus according to claim
 1. 8. A light source apparatus comprising: a first semiconductor light source that has one end and another end; a second semiconductor light source that has one end and another end, with the one end being coupled to the other end of the first semiconductor light source; a current detection resistor that has one end and another end, with the one end being coupled to the other end of the second semiconductor light source; a power source circuit that apply current to the first semiconductor light source, the second semiconductor light source, and the current detection circuit; a current detection circuit that detects current that flows to the current detection resistor and outputs a current detection signal; a control circuit that controls the power source circuit based on the current detection signal; a first bypass circuit coupled in parallel to the first semiconductor light source, the first bypass circuit including a first clamp element that has a first clamp voltage that is higher than a maximum voltage during operation of the first semiconductor light source and a first bypass resistor that is coupled in series to the first clamp element, and applying current when there is an open fault in the first semiconductor light source; a second bypass circuit coupled in parallel to the second semiconductor light source, the second bypass circuit including a second clamp element that has a second clamp voltage that is higher than a maximum voltage during operation of the second semiconductor light source and a second bypass resistor that is coupled in series to the second clamp element, and applying current when there is an open fault in the second semiconductor light source; a first detection circuit that detects an open fault of the first semiconductor light source based on an end-to-end voltage of the first bypass resistor, and a second detection circuit that detects an open fault of the second semiconductor light source based on an end-to-end voltage of the second bypass resistor. 